1. Field of the Invention
The present invention relates to emergency lighting systems and, more particularly, to a novel wireless means for energizing a fluorescent lamp when primary line power has been interrupted by sensing lamp current to charge a storage battery and to connect the battery to the lamp and its conventional ballast via an inverter ballast circuit in response to the power source interruption.
2. Brief Description of the Prior Art
In the past, it has been the conventional practice to provide an emergency energization of a fluorescent lamp by coupling an emergency power source or supply into the lamp circuit. Coupling necessitates the provision and interconnection of external wires from the emergency power unit to the fluorescent lamp and conventional ballast so that the lamp is energized in response to power interruption from the main power source. In addition to the provision and connection of external wires, the emergency power source generally takes the form of a storage battery which is rechargeable and requires a separate charging source connected to line voltage for charging purposes when the line voltage is present.
Another problem resides with the employment of conventional emergency power sources for fluorescent lamps which stems from the fact that the emergency power unit generally cannot be accommodated into a standard fixture inasmuch as the length of a fluorescent tube is fixed and, therefore, the socket connections at the opposite ends of the tube are also fixed. This sometimes necessitiates the provision of mounting the emergency source in the central channel of the shell or reflector portion between adjacent lamps.
Therefore, a long standing need has existed to provide an emergency power source for fluorescent lamps that may be placed in series therewith and be responsive to main power line or source interruption to automatically provide a rechargeable battery power to the conventional ballast and the lamp. Also, a charging circuit is desirable which will recharge the storage battery in the emergency unit directly from lamp current when the lamp is energized during normal operations without interruption of the main power source.